Means for protecting radio receiving sets



`July 31, 1934.

T. D. GIBBS 1,968,198

MEANS FOR PROTECTING RADIO RECEIVING SETS #fiona/Pf 0755.5-

Patented July 31, i934- uri'ran stares @FFHC FOR PRQTECTING RADIORECEVlING SETS 5 Claims.

This invention relates to a protective system and devices for radioreceiving sets. in the conventional receiving set short circuitsoccurring through condenser-s, choke coils, the rectifying tubes, etc.,are frequent. These short circuits overload the power ransforrner andfrequently burn out the secondary windings of the same.

The principal object of this invention is to provide a protective meanswhich will immediately and automatically open the power supply to thetransformer should an accidental short circuit occur.

Another object of the invention is to so construct tne means that shoulda failure or open circuit occur in the plate circuit the power supplywill also be cut olf.

A further object is to provide a visable indicating device which willindicate to the user, at the time of starting the set, whether there areany damaging open or short circuit conditions.

Other objects and advantages reside in the detail construction of theinvention, which is designed for simplicity, economy, and efficiency.These will become more apparent from the following description.

ln the following detailed description of the invention reference is hadto the accompanying drawing which forms apart hereof. Like numeralsrefer to like parts in all views of the drawing and throughout thedescription.

In the drawing:V

Fig. l is a circuit diagram illustrating the power supply circuitfeeding any typical radio receiving set.

Fig. 2 is a detail diagram of the control switch illustrating the switchin the starting position.

Fig. 3 is a similar detail diagram of the control switch illustratingitin the operating or safety position.

In the drawing typical standard partsof a radio power supply circuit arediagrarned and indicated by numeral as follows:` power transformerprimary li), iilarnent secondary windings 11 and l2, power secondarywinding 13, rectifying tube lil. choke coil 15, filtering condensors 16.

The rst filament secondary winding 11 supplies current to the iilamentof the rectifying tube 14. The second larnent secondary winding suppliescurrent to the filaments of the set tubes through a pair of conductors13. The secondary power winding i3 supplies the plates of the rectifyingtube through suitable conductors 39, and supplies current to the gridsof the set tubes and to the speaker field through a suitable conductor Aconductor 19 supplies the radio frequency (Cl. Z-27 screens and thedetector plates. A conductor 20 leads to the power stage of the set. Aconductor 21 supplies the current to the plates of the radio frequencytubes of the set. The alternate cursupply is fed to the primary 10 ofthe power transformer through a pair of conductors 22 and 23.

As thus far described the hook-up comprises a typical power supplysystem of a standard receiving set, In applying the invention to theabove power circuit, an electro-magnet 25 is placed in series with theplate supply conductor 21 so as to actuate a switching armature 24, anda four pole double Contact switch is placed in the current supply line23 to the transformer primary 10.

The switch comprises a first pair of switch blades 32 and 33 and asecond pair of switch blades 28 and 29. The members of each pair may bemade to close Contact with each other by the actuation of aneccentrically mounted switch butto-n 38 of insulating material. Theswitch is connected into circuit by bridging the the blades 23 and 33together and connecting them by means of a suitable conductor 2'7 with acontact 26 which can loe closed by the armature 36. The armature is incircuit with the primary lead 23. The latter lead is connected to theswitch blade 32 through a resistance coil 31. The switch blade 29 isconnected to the primary 10 through a suitable con ductor 30.

A pilot light 34 is provided, or this may be the usual pilot light withwhich all conventional sets are provided. The pilot light 341s connectedto the lament leads 13 or any other suitable source oi energy throughconductors 35. The conductors 35 lead through an armature contact '36and a Contact maker 37 on the armature 24. Thus, a closing movement ofthe armature 24 closes both contacts 26 and 37.

Operation When the set is not operating, the switchv is in the offposition illustrated in Fig. 1. lIt will now be noted that in thisposition, current can not flow from the lead 23 to the conductor 30 andthe primary l0, since the circuit is broken between the armature 24 andthe contact 26. Should it be desired to operate on the set, the button38 is rotated to the starting position of Fig. 2 so as to close thecircuit between the blades 32 and 33 and between the blades 28 and 29.Current can now ilow from the conductor 23 through choke coil 31, theblades 32 and 33, the blades 28 and 29 and the conductor 30 to theprimary 10. This of course energizes the filaments and impresses voltageon the plates. No current however flows through the plate circuit untilthe tube temperatures reach their ionizing points. When the latter pointis reached, current passes through the plate lead 21 and energizes theelectro-magnet 25 to cause it to actuate the armature 24 and close thecontacts 26 and 37. A by-pass is now provided for the primary currentthrough the armature 24 and the contact 26 and the contact 37 to thepilot light. The operator on noting the illuminated pilot light nowturns the switch button 38 to the safety position of Fig. 3 so as tobreak the contact between the blades 32 and 33 and allow all of thecurrent to iiow through the by-pass 24, 26, 27, 28, 29 and 30. The setnow continues to operate until either an accidental short or opencircuit occurs or until the switch is again turned to the o1r'positionof Fig.r l.

Let us assume that metallic particles should cause a short .circuitbetween the plates of the rectifier tube 14. This will immediatelyoverload the secondary and stop or reduce the flow through the platefeed 2l. This will allow the electro magnet 25 to release the armature24 and immediately break the .circuit through the primary l0, Any otheraccidental interruption which. would reduce or stop the flow through theconductor 2l, such as a burnout in the choke coil l5, a cross circuit inthe condensers 16, etc., will similarly open the feed circuit.

It is desired to call attention to the fact that the armature 24'doesnot move immediately upon the closing the feed circuit to the primary10, since it requires an appreciable time for the electronic current toflow. The operator, however, is always advised of the termination ofvthis time interval by the illuminating of the pilot light 34 so that hemay allow suiiicient interval before turning the switch to the safetyposition of Fig. 3. The heaviest current flow or greatest currentconsumption in the set is at the instant the set is turned on. The surgeof current is damaging to the feed conductors, transformer, house fusesetc. The resistance coil 31 acts to reduce the initial potential to a'safe amount and, since the coil is out of service during the operativeposition of the switch, the operation of the set is not interfered with.

While a specific form of the improvement has been described andillustrated herein, it is desired to be understood that the same may bevaried, within the scope of the appended claims, without departing fromthe spirit of the invention.

Having thus described the invention, what is claimed and desired securedby Letters Patent 1s:-

1. Means for breaking the primary -circuit of the power transformer of aradio receiving set should the secondary of said transformer becomeoverloaded comprising: Van electro-magnet in series with said secondary;an armature actuated by vsaid magnet; a contact arranged to be closed bythe actuation of said armature, said contact being in series with thesupply to said primary; a manually actuated switch bridged across saidated by said magnet; a contact arranged to be closed by the actuation ofsaid armature, said "contact being in series with the supply to saidprimary; a manually actuated 'switch bridged across said contact; and achoke coil in series with said switch so as to be bridged by the actionof said armature and contact.

3. Means for breaking the primary circuit of vthe power transformer of aradio receiving set should the secondary of said transformer becomeoverloaded comprising: a conductor conducting the secondary current fromsaid secondary to the plate circuit of said set; an electro-magnet inseries with said plate circuit; an armature adapted to `be actuated bysaid electro-magnet; a contact adapted to be closed by said armature; afirst circuit to said primary; a manually operated switch in said rstcircuit; a second circuit to said primary through said armature and saidcontact; and a switch for throwing either or both said first and secondcircuits in series with said primary.

4. Means for breaking the primary circuit of the power transformer of aradio receiving set should the secondary of said transformer becomeoverloaded comprising: an electro-magnetic switch in series with saidsecondary; a first pair of switch blades; a second pair of switchblades; means for closing both or either of said pairs of switch blades;a conductor connecting one member of each pair to said magnetic switch;a second conductor connecting Yanother of said switch blades to saidmagnetic switch and to a source of current; a third conductor connectingthe remaining switch blade to said primary; and means -for closingeither or Iboth said pairs Aof switch blades as desired.

5. Means for breaking the primary circuit of the power transformer of aradio receiving set should the secondary of said transformer becomeoverloaded comprising: an electro-magnetic switch in series with saidsecondary; a first pair of switch blades; a second pair of switchblades; means for closing both or eitherof said pairs vof switch blades;a conductor connecting one member of eachpair to said magnetic switch; asecond conductor connecting another of said switch blades to saidmagnetic switch and to a source of current; a third conductor connectingthe remaining switch blade to said primary; means for closing either orboth said pairs of switch 'blades as desired; and a pilot light arrangedto be illuminated in consequence of the closing of said magnetic switch.

THEODORE vD. GIBBS.

